Flow control of gas through an internal combustion engine has been used in order to provide vehicle engine braking. Generally, engine braking systems may control the flow of gas to incorporate the principles of compression-release type engine braking, exhaust gas recirculation, exhaust pressure regulation, and/or bleeder type engine braking.
The operation of compression release-type engine braking or retarder systems is well-known in the art. A compression release engine brake decreases the kinetic energy of an engine by opposing the upward motion of the engine's pistons on the compression stroke. As a piston travels upward on its compression upstroke, the gases that are trapped in the cylinder are compressed. The compressed gases oppose the upward motion of the piston. During engine braking operation, as the piston nears the top of its stroke, an exhaust valve is opened to release the compressed gasses in the cylinder to the exhaust manifold. After the pressure has been released from the cylinder, the piston cannot recapture the potential energy stored in the compressed gases on the subsequent expansion down-stroke. Instead, the energy is dissipated through the exhaust and radiator systems of the engine. By dissipating the energy developed by compressing the cylinder charge, the engine develops retarding power to help slow the vehicle down.
The operation of a bleeder type engine brake has also long been known. During engine braking, in addition to the normal exhaust valve lift, the exhaust valve(s) may be held slightly open continuously throughout the remaining engine cycle (full-cycle bleeder brake) or during a portion of the cycle (partial-cycle bleeder brake). The primary difference between a partial-cycle bleeder brake and a full-cycle bleeder brake is that the former does not have exhaust valve lift during most of the intake stroke.
Compression release and/or bleeder type engine braking systems provide the operator with increased control over the vehicle. Properly designed and adjusted engine braking systems can generate retarding power equal in magnitude to a substantial portion of the power generated during positive power operations and may supplement the braking capacity of the primary vehicle wheel braking system. Accordingly, engine braking systems may substantially extend the life of the primary wheel braking system of the vehicle.
The principles of exhaust gas recirculation (EGR) are also well known. An EGR system allows a portion of the exhaust gases to flow back into the engine cylinder. Generally, there are two types of EGR systems, internal and external. External EGR systems recirculate gases from the exhaust port to the intake port through external means, such as, for example, external piping. Internal EGR systems recirculate exhaust gases back into the engine cylinder through an open engine valve(s).
EGR is useful during both positive power and engine braking operation. During positive power, EGR is primarily used to improve emissions by reducing the amount of NOx created by the engine. During engine positive power, one or more intake valves may be opened to admit fuel and air from the atmosphere, which contains the oxygen required to burn the fuel in the cylinder. The air, however, also contains a large quantity of nitrogen. The high temperature found within the engine cylinder causes the nitrogen to react with any unused oxygen and form nitrogen oxides (NOx). Nitrogen oxides are one of the main pollutants emitted by diesel engines. The recirculated gases provided by an EGR system have already been used by the engine and contain only a small amount of oxygen. By mixing these gases with fresh air, the amount of oxygen entering the engine may be reduced and fewer nitrogen oxides may be formed. In addition, the recirculated gases may have the effect of lowering the combustion temperature in the engine cylinder below the point at which nitrogen combines with oxygen to form NOx. As a result, EGR systems may work to reduce the amount of NOx produced and to improve engine emissions. Current environmental standards for diesel engines, as well as proposed regulations, in the United States and other countries indicate that the need for improved emissions will only become more important in the future.
It is therefore an advantage of some, but not necessarily all, embodiments of the present invention to provide improved emissions by reducing the amount of NOx created by the engine.
An EGR system can also be used to improve the effectiveness of engine braking. Recirculating gas during engine braking operation permits higher pressure gas from the exhaust manifold to recirculate back into the engine cylinder. The recirculated gas increases the total gas mass in the cylinder at the time of a subsequent engine braking event, thereby increasing the braking effect realized by the vehicle. By controlling the pressure and temperature in the exhaust manifold and engine cylinder during engine braking cycles, the level of braking may be optimized at various operating conditions. The use of EGR during engine braking may be referred to as braking gas recirculation, or BGR.
It is therefore an advantage of some, but not necessarily all, embodiments of the present invention to improve engine braking using gas recirculation and to provide different levels of engine braking and to optimize engine braking with engine speed.
EGR systems (valves, inter-coolers, passages, etc.) tend to become sooted over their life-cycle. Soot accumulation can reduce the overall performance of the system, and could cause failure of various system components. This condition may lead to decreased fuel economy, and even possible emissions compliance issues. The primary approach to this problem has been to institute regular maintenance and cleaning intervals, which may be undesirable to the long-haul heavy duty truck business. It is also problematic because of the physical difficulty involved with the cleaning of this system.
It is therefore an advantage of some, but not necessarily all, embodiments of the present invention to provide a method and apparatus for cleaning gas recirculation system components.
Additional advantages of various embodiments of the invention are set forth, in part, in the description that follows and, in part, will be apparent to one of ordinary skill in the art from the description and/or from the practice of the invention.